1. Field of the Invention
The present invention relates to a packet retransmission method and apparatus in a mobile communication system. More particularly, the present invention relates to a method and apparatus for processing, when a base station requests a terminal for packet retransmission in Contention-Based Access, the packet retransmission request.
2. Description of the Related Art
Mobile communication systems developed to provide the subscribers with voice communication services on the move. With the rapid advance of technologies, the mobile communication systems have evolved to support high speed data communication services as well as the standard voice communication services. However, the resource shortage and user requirement for higher speed data services spurs the evolution of the mobile communication system to more advanced system.
For this purpose, researches are being conducted in various aspects and, particularly, focused on the retransmission process in the situation of packet transmission failure to guarantee communication reliability.
As the retransmission technique, there are HARQ (Hybrid Automatic Repeat reQuest) operating at physical layer level and ARQ (Automatic Repeat reQuest) operating at RLC (Radio Link Control) layer level. The ARQ technique is of correcting errors through data retransmission, while the HARQ technique is of attempting error correction to the received data and determining whether to perform retransmission using error detection code.
Meanwhile, when the terminal (transmitter) transmits a packet to a base station (receiver), the transmission can be performed in one of contention free access using the resource dedicated to the terminal and contention-based access using the resource accessible by multiple terminals.
However, there is no packet retransmission technique developed for use in the contention-based access yet. In the case of using the legacy HARQ retransmission method in the contention-based access, the terminal has to waits HARQ RTT (Round Trip Time) of 8 ms to perform retransmission since the detection of the retransmission necessity, resulting in retransmission delay problem.
Also, the HARQ retransmission mechanism operates in such a way that the retransmission is performed on the same uplink resource as the previous attempt in the same process. Accordingly, if the HARQ retransmission mechanism is applied to the contention-based access procedure, the terminals attempt retransmission using the same resources so as to cause collision.
There is therefore a need of an efficient packet retransmission method for use in the contention-based access procedure.